US1639531A - Refining of hydrocarbon oils - Google Patents

Description

Patented Aug. 16, 1927.-`

4UNITED vs'rn'iiss .ERNEST B. PHILLIPS, OF EAST CHICAGO,

AND JAMES G. STAFFORD, OF WHITING,

INDIANA, ASSIGNORS TO SINCLAIR REFINING COMPANY, OF CHICAGO, ILLINOIS,

A CORPORATION OF MAINE.

REFINING 0F HYDROCARBON OILS. Application illed October 22, 1924. Serial No. 745,185.

This invention relates to an improved method of refining and distilling hydrocarbon oils, such as petroleum and the various fractions and distillates derived from petroleum; and more particularly relates to the treatment of oils which have been subjected to refining treatment with sulfuric acid.

One of the general methods employed inl refining hydrocarbon oils is to treat the oil with sulfuric acid and follow this acidtreatment with a neutralization treatment with caustic alkali succeeded by a water wash. Complete neutralization followed by complete washing would presumably completely remove'the sulfuric acid bodies introduced into the oil by the acid treatment, but in the practical application of the methods hitherto employed neither the neutralization nor the washing are complete and the treated oil usually contains some of the original sulfuric acid bodies as well as some of the reaction products of the alkali treatment. When oil containing such con'stituentsis distilled in the ordinary way these constituents 5 are -decomposed and constituents causing a persistent discoloration of the oil are formed. The constituents left in t-he oil by imperfect refining apparently include compounds such as the alkyl sulphates and alkali compounds thereof which are decomposed with the liberation of sulfur dioxide at the temperature of distillation, the sulfur dioxide so liberated reacting upon other constituents of the oil, probably certain unsaturated compounds,

r to form the compounds causing the discoloration. Cracked oils, such as pressure distillates, contain more or less unsaturated hydrocarbons, and discoloration of the character referredl to is particularly noticeable when cracked oils. or blended fractions containing appreciable percentages of cracked oils, are treated in the ordinary way. The fcracked and unsaturated constituents which apparently contribute to this discoloration are valuable constituents of motor fuel, and it is one of the important advantages of the present invention that it provides a method of refining oils containing cracked constituents with the production of a product of good color without requiring the removal of the unsaturated constituents. An improved yield as well as an improved product is thereby obtained.'

treatment.

This invention includes an im roved methodI of treating oils, particular y oils containing cracked constituents, which have been subjected to refining treatment with sulfuric acid and a combined refining operati onlincluding treatment with sulfuric acid. The invention also includes an imp-roved method of treating oils with alkali, and a combined redistillation and alkali refining The invention also includes an improved distilling and refining operation and an improved method of operating reflux towers.

According to the present invention, the hydrocarbon oils are distilled and subjected to treatment with an alkali while undergoing retluxing in a tower from which refiux is returned to the still in which the .distillation vis effected. The alkali is introduced into the reflux tower and is brought into intimate contact with the liquids and vapors in the tower and the oil is subjected to treat- F The alkali may be introduced into the rel uX tower in the form of an aqueous solution or suspension, or such a solution or suspension may be introduced in admixture with oil. The alkali may with advantage be introduced into the tower in the form of an emulsion with all or part of the oil subjected to distillation to assist and promote the distribution of the alkali in the tower.

In the further treatment of oils which have been treated with sulfuric acid, the in troduction of alkali into a redux tower on the still in which the oil is subjected to distillation affords several special advantages. The alkali combines with acidic constituents liberated by decomposition of any sulfuric acid bodies in the oil, including any present in the gaseous state such as sulfur dioxide, to form compounds stable at the prevailing temperatures. Objectionable reaction bel the residual oil left in the still is slightly alkaline, but only slightly alkaline, particularly where an externally heated still is ein. ployed. By restricting the amount of alkali employed in this way, the excess alkali and vthe reaction products of the alkali treatment may be withdrawn in suspension in the residual oil in the still. Apparently gums o r resins a're formed by the same ecoinposition which liberates acidic constituents from the sulfuric acid compounds which associate with any excess alkali and with the compounds formed with the alkali 1n such a manner that they are maintained in suspension in the oil. After withdrawin ing the residual oil and on stan ing, a deposit including sulfurous and sulfuric compounds with the alkali separates. If such deposits are allowed to form on an externally heated surface destructive overheating of the still walls may result and a glassy coating tends to form which is very dilicult to remove but by regulating the amount of alkali employed, .deposition in the still may be prevented. While this feature of the invention is of particular advantage in preventing the formation of Such deposits on the interior of externally heated stills, it is also useful in connection with the operation of stills which are internally heated, such as steam stills, and provides a method for removing any excess alkali and the reaction products of the alkali treatment in a continuous or semi-continuous manner.

In one way of carrying out the process of the present invention, the oil subjected to distillation is introduced into the still through the reflux tower. The alkali may be introduced in admixture with the oil or separately. The oil is thus subjected to treatment with the alkali as it is brought to the temperature of distillation by heat interchange with the hot vapors and liquids in the tower, and a substantial part of the lighter constituents of the oil may be distilled in the tower before decomposition of the sulfuric acid bodies begins. Then such decomposition begins, the alkali yimmediately combines with the acidic constituents liberated by the decomposition, and that part of the oil which is distilled before the decomposition begins is thus effectively kept from contact with the decomposition products. The operation may be regulated so that the major part of the distillation is effected in the tower and the entire refining and distilling treatment and cool- .of the major part of the distillatey carried out in the tower. y

The process of the invention is of special value and application in rerunning or redistilling' light oils and distillates, sucn as naphtha character distillates and pressure distillates or mixtures or blends of such distillates and fractions, for the separation of a finished product without further refining treatment, partieularlywhere such oils or distillates have previously been subjected to chemical refining treatment.

The invention will be further described in connection with the accompanying drawing, which illustrates, somewhat diagrammatically and conventionally, one arrangement of apparatus adapted for carrying out the process of the invention, but it is intended andwill be understood that this specic' illustration and description are for the purpose of exemplification and that the invention is not limited thereto.

The accompanying drawing illustrates, partly in section and partly in elevation, a still, reflux tower, and appurtenances arranged for carrying out the process of the invention.

Referring to the drawing, the still 1 is of the shell type, externally heated by the llot products of combustion from the fire box 2 passing over the lower part of the still shell to the exit flue 3. The still is provided with a charging line 4 for the introduction of fresh oi] and a drawoll line 5 arranged for discharging residual oil from the still. Arranged above the still, and directlyy ccmlnunicaiing with the vapor space therein, is a reflux tower 6 provided with a helical baille 7 Vapors escape from the upper end of thev reflux tower through the vapor line 8 to the condenser 9 where they are cooled and condensed. The condensing coil, or coils, in the condenser 9 discharges through connection 10 into the look-box 11 where a separation of the condensed distillate and any uncondensed vapors and gases is effected. From the look-box the condensed distillate is discharged into a rundown tank or any other suitable receptacle through the connectien 12, and the uncondensed gases and vapors are withdrawn through connection 13. The still and reflux tower may be provided with suitable heat insulation.

T he reflux tower shown in the drawing is of the general type described and illustrated in an application of John E. Bell, filed April 1, 1924, Serial No. 703,338, and reference may be made to this application for a more complete description of the construction of this type of tower. The present invention is of special value and application in conv nection with towers of this type. and in connection with certain methods of distillation described in the said application. but it will be understood that the process of the invenllf) tion may also be employed 'in connection with reflux towers of other suitable construction and arrangement.

A connection 14 is arranged somewhat below the top of the tower for the introduction of oil, and a connectionl at a somewhat lower point on the tower for the introduction of caustic alkali in admixture with fresh oil. A tank 16 is arranged for supplying the solution of alkali. From this supply tank, the solution of alkali is fed into a feed tank 17 provided with a gauge glass 18 from which the flow of caustic solution can be regulated by means of valves 19 and 20. The How of caustic solution can also be regulated by means of a weir 21 discharging into connection 22.

A centrifugal pump v23 is arranged for discharging` fresh loil into the reflux tower through connection 15, and connection 22 is arranged on the inlet side of the pump for admixing the solution of alkali with the fresh oil entering the pump through the connection 24. In the pump, the oil and the solution of alkali are beaten into an emulsion which is of such a character that the solution of alkali is held in suspension in the oil more or less evenly distributed therethrough, and the oil and alkali are introduced into the tower in intimate intermixture. A centrifugal pump is of particular advantage for conjointly introducing the solution of alkali with a part or all of the oil to be introduced into the tower, but pumps of other construction and operation, such as reciprocating pumps, may be employed, or the solution of alkali may be introduced into the tower by means of a separate pump.

In carrying out the process of the invention in the apparatus illustrated, an initial charge of oil is introduced into the still 1 through the charging line 4 and the still charge is brought to the appropriate ten'ipcr- .ature for effecting the distillation. As vapors form in the still they pass upwardly through the helical passage in the tower wherethey are cooled b v the fresh oil ini roduced into the upper end of the tower. After the still is brought to the distillation tempera-ture, fresh oil, in. admixture with an appropriate amount of an alkali. such as caustic soda. is introduced through connection 15 and flows d-ownwardly over the helical b-aiile in the tower in direct contact and in heat exchanging relation with the vapors from the still. The amount of oil is relatively much larger than the amount of alkali employed. and b v introducing the alkali intimately dispersed through the oil in the form of a emulsion the distributi ,'n of the alkali in the tower is promoted. ere an aqueous solution of alkali is emploved, the water is evaporated in the tower anda part of the oil is also vaporized, so that the concentration of the alkali increases as the mixture of oil and alkali flow downwardly. From the tower, the unvaporized oil, any excess alkali and any compounds formed with the alkali by reaction in the, tower enter the still. The vapors liberated in the still and in the tower escape to the condenser 9 after being subjected to treatment with the alkali in the tower. Residual oil is drawn off, either intermittently or continuously, through the draw-off 5 to maintain thestill charge at the desired point as the operation progresses. By appropriate contrel of the amount of alkali employed, any excess alkali and the reaction products of thc treatment with alkali may also be drawn off, in large part, with the residualoil.

In the treatment of an oil whiclnhas been subjected to refining treatment with sulfuric acid, the oil and the alkali are advantageouslv introduced near the top of the tower, for example at a point about one third or one fifth of the heighth below the top of the tower or less. An increased amount of the distillation may thereby be effected in the tower before decomposition of sulfuric acid bodies begins. For example. in rerunning for a refined gasoline fraction a naphtha character .fraction or a pressure distillate which has been subjected to acid treatment, the oil may be introduced into the tower at a point about one third below the top in admixture with the alkali. As the oil and alkali travel downwardly through the tower the lower boiling fractions are released and escape as'a vapor. Decomposition of the sulfuric acid bodies, as such or as compounds with the alkali, may not begin above a point two thirds of the way down the tower, and the alkali which is present in increasing concentration immediately combines with the acidic constituents as they are formed. The introduction of the alkali near the top of the tower also provides an increased opportunity for contact between the alkali and the vapors and liquids in the tower.

' The amount of alkali employed, although always small in relation to the amount of oil, may vary widely and depends upon the character of the oil as well as its previous treatment. It is advantageous to employ an amount of alkali sufficient to render the residual oil in the still barely alkaline but insuflicient to cause deposition in the still.

This amount-may be readily determined by test in any given case.

To assist in controlling the operationof the. reflux tower, a regulated amount of an oil or distillate having an average boiling point corresponding to that of the desired distillate, or having a somewhat lower average boiling point, may be introduced into the upper end of the tower through the connection 14. In another way of carrying out the invention, such alight character fraction 4may be introduced in 'admixture with the principalfeed to the upper end of the tower, but it is more advantageous to introduce it at a point between the point of introduction of the principal feed and the point where the vapors escape from the tower. A part of the condensed distillate from the operation may be employed for controlling the operation of the reflux tower in this way. By introducing a light fraction in this manner, an increased cooling is effected in the upper end of the tower due to the vaporization of the light fraction and an improved fractionation is effected. Heavy constituents which might otherwise escape with the vapors are condensed by the cooling effected while the light fraction which is vaporized corresponds to the desired distillate and does not introduce any heavy constituents into the distillate. The operation of the reflux tower may also be controlled in this way where the principal feed is introduced directly into the still without passing through the reflux tower. The improved control of the refluxing operation thus afforded further assists in directly producing a completely refined product..

The process of the invention may be carried out in much the same way in a steam still. In either a steam still or an externally heated still, steam may be introduced directly into the oil in the still, but if direct steam is employed it is preferably held to a minimum.

The treatment of the oil with sulfuric acid prior to the distillation may be carried out in the ordinary way. T he oil, for example. may be agitated with sulfuric acid, washed with water, subjected to a neutralizing treatment with alkali, again washed with water, and then'subjected to the improved refining and distilling process of the present invention. The neutralization treatment-may be omitted and the oil subjected to distillation according to this invention immediately after the acid treatment. although where the process is carried out in this manner, it is preferable to subject the acid treated oil to a thorough washing treatment with water hefore it is introduced into the still. Where a neutralizing treatment is employed, a less extended water wash may be employed thereafter or the subsequent water wash may be omitted. In the treatment of oils containing cracked constituents, the rigor of the acid treatment may be reduced. for example the period of treatment may be shortened or a lesser amount of acid or a dilute acid employed, in order to retain in the finished product the olefines and naphthenic constituents.

The process of the present invention is of special value and application in connection with continuous processes of refining oils with sulfuric acid, and enables such processes.

to be employed without sacrifice in Ithe quality ofthe product and without impracticably close regulation. The continuous refining method may be carried out for the maximum throughput and any small amounts of acid bodies left in the oil, due either to imperfect neutralization or imperfect washing, may be disregarded.

Other fixed alkalies, such as potassium hydroxide and calcium hydroxide, are also useful in carrying out the processof the present invention.

In its broader aspects, it will be evident that the invention provides an improved method of refining hydrocarbon oils with alkalies whereby t-he oil is subjected to treatment with the alkali in both the vapor and the liquid phase while undergoing a refluxing operation. It will also be seen that the invent-ion provides an improved refining and distilling operation of particular advantage for treating oils, especially oils containing cracked constituents, which have been subjected to a refining treatment with sulfuric acid.

'We claim:

l. An improved method of operating reflux towers on oil stills which comprises passing oil vapors through the tower and introducing fresh oil into the tower in direct contact with the vapors therein in the form of an emulsion with a relatively small amount of an aqueous solution of an alkali.

2. An improved method of refining hydrocarbon oils which comprises distilling the' oil in a -still provided with a reflux tower, emulsifying a relatively small amount of an aqueous solution of an alkali in fresh oil to be distilled. and introducing the emulsion into the reflux tower.

3. An improved method of distilling and refining hydrocarbon oils, which comprises distilling the oil in a still provided with a reflux tower, introducing fresh oil directly into the tower, introducing an alkali directly into the tower, and conducting reflux, the unvaporized fresh oil and the alkali from the tower to the still.

4. An improved method of distilling and refining hydrocarbon oils, which comprises distilling the oil .in a still provided with a refiux tower, introducing an alkali directly into the tower, introducing fresh oil to be refined and distilled directly into the tower, introducing an oil having an average boiling point not substantially higher than that of the desired distillate directly into the tower at a point not substantially lower than the point at which the said fresh oil is introduced, and conducting reflux, unvaporized oil and the alkali from the tower tothe still.

5.' An improved method of distilling and refining hydrocarbon oils. which comprises distilling the oil in a still provided with a reflux tower, introducing an alkali, fresh oil to be refined and distilled, and a lighter oil into the tower in direct contact with the vapors and liquids therein, and conducting refiux, unvaporized oil and the alkali from the tower to the still.

6. A combined operation for refining and distilling hydrocarbon oils, comprising subjecting the oil to a distilling operation, subjecting the distilled vapors to a refluxing operation in direct contact with an alkali supplied to the refiuxing operation, conveying reflux and the alkali from the refluxing operation to the distilling operation, withdrawing vapors from the refiuxing operation and withdrawing residual oil from the distilling operation.

7 An improved method of distilling and refining hydrocarbon oils, which comprises distilling the oil in a still provided with a reflux tower, and returning reflux from the tower to the still, and introducing an alkali into direct contact with the vapors and liquids in the tower in amount sufficient to render the residual oil in the still slightly alkaline.

8. An improved method of distilling and refining hydrocarbon oils, which comprises distilling the oil in a still provided with a reflux tower, introducing an alkali into the tower in direct contact with the vapors and liquids therein, conducting reflux from the tower to the still, and withdrawing excess alkali and reaction products of the alkali treatment in suspension in the residual oil from the still.

9. An improved method of treating hydrocarbon oils which comprises subjecting the oil to refining treatment with sulfuric acid, subjectin a body of oil to distillation in a still provided with a reflux tower, introducing the acid treated oil into the upper end of the tower, introducing an alkali into the upper end of the tower, and conducting reflux, unvaporized oil and alkali from the reflux tower to the still.

10. An improved method of refining hydrocarbon oils which comprises distilling the oil in a still provided with a reflux tower, intimately admixing a relatively small amount of an alkaline refining agent with fresh oil, and introducing the mixture into the reflux tower in direct contact with the vapors therein.

11. An improved method of treating hydrocarbon oils which comprises subjecting the oil to refining treatment with sulphuric acid. subjecting a body of oil to distillation in a still provided with a reflux tower, and introducing the acid treated oil and an alkali into the upper end of the tower in dir/ect contact with the vapors therein. n

In testimony whereof we alix our signatures.

ERNEST B. PHILLIPS. JAMES G. STAFFORD.

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